Verified by 
In the summer of 2004, Singapore Airlines commenced its marathon non-stop SQ21 service from Newark to Singapore. The flight covers a distance of 9,500 miles (15,300 km) and the plane remains aloft for 18 hours. Flight SQ21 is still the longest non-stop passenger service by a considerable margin.
We live in a fragmented age. People seldom spend 18 consecutive hours in the same enclosed space, and when they do, it's rarely by choice. Prison sentences, debilitating illnesses, and epic blizzards force people to occupy the same space for hours on end, but long haul flights differ because people choose to endure them for the privilege of rapidly traversing continents.
As a sometime resident of three cities on three continents (New York City; Sydney, Australia; Johannesburg, South Africa), each city separated from the other two by at least 7,000 miles, I've made that choice many times before. Perhaps what fascinates me most about the experience of long haul flights is how they distort our perception of time. (For more on the perception of quantity, see my earlier blog post.) For example, take the daylong journey between New York and Sydney: the first leg between New York and Los Angeles passes in 6 hours, the second leg between Los Angeles and Sydney drags on for another 15 hours, and a relatively brief break separates the two legs. How do we perceive each hour of the journey? Does the first hour seem just as long as the final hour? What about the hours in the middle? Simply put: are all hours endured in economy class created equal?
The short answer is: no, humans don't perceive time objectively. Common wisdom suggests that good days pass too quickly, and days waiting for loved ones to return from war pass too slowly. And what of the journey from New York to Sydney? I've asked other passengers, and they seem to agree that time passes something like this: the first hour is agonizingly slow, the second hour passes more quickly, and the remaining hours of the first leg pass more and more quickly. The same applies when you embark on the second leg: the first few hours drag, but somewhere between the 13th and 21st hours of your journey, a black hole swallows time entirely. When you look back on the journey, you remember every minute of the first hour, but nothing of the six or seven hours in the middle. Then, excitement builds as you near your destination, and the hours correspondingly slow to a crawl.
Not everyone experiences the journey the same way, of course, but no one experiences time as it truly passes, with each hour seeming just as long (or short) as every other hour.
Quirks of time perception aren't limited to air travel of course. Children are often confused when their parents claim that time passes too quickly, because the passage of time really seems to accelerate as we age. Researchers draw on many theories to explain the quickening of time: our youthful years are peppered with novelty, and the richness of novel experiences means they pass by more slowly than do experiences that command little attention and hold little interest. Another reason is that time perception is relative, so a year represents a monumental 20% of your life when you've been alive for five years, but only 2% when you've been alive for fifty years. It's also possible that we tend to be busier as we get older, and who has time to monitor the time when we're already short on time?
This classic New Yorker cover from 1976 illustrates a principle of distance perception that also describes our perception of time: we're more sensitive to the passage of time in the near future than in the distant future. 
If I offered to give you a chocolate bar, and then immediately retracted my offer and instead promised to give you the chocolate bar in an hour, you'd probably be displeased. You'd be less concerned if I offered to give you the chocolate bar in exactly one week, but then pushed my offer back a further hour. I'm still frustrating your desire for chocolate by an hour, but an hour without chocolate right now is far more distressing than imagining an extra hour without chocolate one week from today.
There's still plenty we don't understand about how humans perceive time, but one fact is clear: we don't perceive time the way clocks portray time, one second at a time, with each second passing just as quickly as its earlier and later counterparts. Indeed, clocks prolong the pain of an already too lengthy experience. Patrick Smith, an erstwhile pilot and author at Salon.com, described just this pain when he remembered the experience of traveling from New York to Johannesburg. Smith remembered that the flight lasted exactly 14 hours and 46 minutes, because he sat directly behind a small digital timer that registered each minute as the plane slowly crossed the Atlantic.
